Orthodontic brackets are typically small, slotted devices for use during orthodontic treatment. The brackets usually are configured for attachment to the front surfaces of teeth, either by directly cementing the bracket to a tooth surface or by bonding the bracket to a metal band that encircles the tooth, though they also may be attached to the back surfaces of teeth. The slots in the brackets, which may be referred to as archwire slots or archwire passages, are disposed horizontally or generally horizontally and are configured to receive an archwire. Traditionally, an archwire is a resilient, curved piece of wire that may be bent or twisted prior to installation in the bracket slots, with an archwire typically extending through the slots of all of the orthodontic brackets that are attached to a patient's upper or lower teeth. The engagement between the archwire and the brackets creates corrective, or prescriptive, forces that are directed to the teeth by the orthodontic brackets to urge the teeth into a correct or desired alignment or occlusion.
The archwire may be secured in a bracket's archwire slot by a variety of mechanisms, such as depending on the bracket's configuration. For example, a “ligating” bracket typically requires a separate fastener, such as a ligature wire or elastic band, which is tied or otherwise positioned around ligating structures, such as tie wings, on the bracket body to secure the archwire in place. A “self-ligating” bracket, on the other hand, typically includes a clamp, gate, or other self-locking closure mechanism, such as a closeable bracket slot, that allows such a bracket to retain the archwire without requiring the use of ligatures or other separate fasteners.
Expressed in slightly different terms, conventional ligating and self-ligating orthodontic brackets define an archwire slot with an opening into which the archwire may be inserted into the slot (other than by axially inserting the archwire through the opposed ends of the archwire slot). The opening of the archwire slot typically extends in a plane generally parallel to the base of the bracket and/or surface of the corresponding tooth to which the bracket is secured. The archwire typically is inserted into the archwire slot by inserting the wire through the opening. However, a conventional ligating bracket requires a ligature or other structure that is not part of the bracket to obstruct or otherwise close the opening to prevent removal of the archwire therethrough. In contrast, a conventional self-ligating bracket includes a movable gate or closure that is coupled to the body of the bracket for relative movement with respect to the body without removal or separation of the gate or closure from contact with the body. The gate or closure is configured to be slid, pivoted, or otherwise moved from an open position, in which an archwire may be inserted into the archwire passage through the opening, to a closed position, in which the opening of the archwire passage is closed or otherwise obstructed to prevent removal of the archwire therethrough.
Regardless of whether the bracket is a self-ligating bracket or whether the bracket requires separate fasteners or ligatures to secure an archwire in the bracket's archwire slot, orthodontic treatment of a patient's teeth typically requires periodic adjustment of the forces that are imparted to the patient's teeth by the installed orthodontic brackets, archwire(s), etc. These adjustments may include changing the magnitude and/or direction of the forces that are imparted to the patient's teeth, such as to adjust the degree to which torque, tip, and/or rotational forces are imparted to the patient's teeth to change the angulation, inclination, rotation, height and/or location of the teeth in order to move the teeth toward an optimal occlusion. As used herein, tipping forces refer to forces applied to the tooth in the mesio-distal direction. Thus, tipping forces may impact angulation. Torsional forces refer to forces applied to the tooth by an archwire that is in torsion within the archwire passage. Thus, torsional forces tend to rotate the tooth in the bucco-lingual direction and may impact inclination. Rotational forces refer to applied forces that tend to rotate the tooth about its long axis.
Adjustment of some of these forces, including torsional (i.e., torque) forces, typically requires removal of the archwire from the corresponding brackets, along with replacement of the archwire and, in some cases, removal and replacement of the bracket. Even with a bracket that permits the applied forces to be adjusted without removal of the bracket from a patient's tooth, fine adjustment of these forces still may be challenging.